store new user to the database

Motivation:

All authenticated user should be store into cerebrum data-storage (neo4j). At the momement this is not the case.

Modification:

• ensure that when the autheticated user hit /api/v0/users/whoami and the user is unknown to cerebrum, a new user will be created.
• add findByEmailAndSub method in the user repository to search the database if user with the supplied email and sub exist
• add a createEnity method inside CerebrumService interface that are implemented inside CerebrumServiceBase abstract class. This will be use when the uri location is not needed.

Result:

Unkown user that have been authenticated will be store by cerebrum.

Target: master